Hold-type display devices such as liquid crystal display devices have a problem that when displaying images in motion, outlines of moving objects are shown blurred (hereinafter, this phenomenon is referred to as a motion blur). As a method for preventing such a motion blur from occurring, a method of increasing a frame rate by interpolating a new frame between two consecutive frames (frame rate conversion process) is known. Further, there is also known a method of performing motion compensation using a motion vector when performing the frame rate conversion process, in order to effectively prevent the motion blur.
Aside from this, as a method for reducing noises included in a motion picture, a recursive noise reduction process using a motion vector is known. FIG. 13 is a block diagram illustrating a configuration of a noise reduction device described in Patent Document 1. In a noise reduction device 110 illustrated in FIG. 13, a frame memory 116 included in a motion-detecting frame-cyclic noise reduction means 111 stores an output video signal of a previous frame. A vector detection means 117 obtains a motion vector MV and a motion component MC (an amount indicating a change in corresponding pixels) based on an input video signal and the output video signal of the previous frame output from the frame memory 116. A cyclic feedback amount control circuit 112 obtains a cyclic coefficient k based on the motion component MC. A multiplier 113 multiplies a pixel value included in the input video signal by (1−k), a multiplier 114 multiplies a corresponding pixel value (a pixel value read from the frame memory 116 using the motion vector MV) by k, and an adder 115 adds outputs from the multipliers 113 and, 114. An output from the adder 115 is output outside the noise reduction device 110 as an output video signal, and stored in the frame memory 116 in preparation for a process to an input video signal of a next frame. According to the noise reduction device 110, it is possible to reduce noises uncorrelated along a time axis (flickering noises), and to prevent an occurrence of a residual image in a motion area, and whereby a clear and high-quality image can be obtained.
Further, a method of combining the frame rate conversion process using motion compensation and the recursive noise reduction process using a motion vector is considered. FIG. 14 is a block diagram illustrating a configuration of an image processing device for performing a frame rate conversion process and a recursive noise reduction process. In an image processing device 120 illustrated in FIG. 14, a frame memory 121, a motion vector detecting unit 122, an interpolated image generating unit 124, and a time base converting unit 125 perform a frame rate conversion process based on motion compensation. A three-dimensional noise reduction processing unit 123 performs a recursive noise reduction process using a motion vector detected by the motion vector detecting unit 122. According to the image processing device 120, it is possible to prevent motion blurs that occur in a hold-type display device, as well as to display a high quality motion picture by performing noise reduction without giving a sense of presence of residual images when displaying a motion picture. In addition, by using the motion vector detecting unit 122 commonly both in the frame rate conversion process and the recursive noise reduction process, it is possible to reduce a circuit size and a memory capacity.